RESUMEN Entre las malezas que interfieren en el crecimiento y desarrollo del sorgo dulce se destaca el amor seco, especialmente por presentar alta capacidad competitiva por los recursos disponibles en el medio. El objetivo de este estudio es comparar la capacidad competitiva del sorgo dulce (Sorghum bicolor) frente al papunga (Bidens pilosa), en función de la proporción de cultivo y planta. Los experimentos se realizaron en un invernadero en un diseño completamente al azar, con cuatro repeticiones. Los tratamientos se organizaron en series de reemplazo en las proporciones de 100: 0, 75:25, 50:50, 25:75 y 0: 100% (sorgo: maleza) que correspondieron a 20:0, 15:5, 10:10, 5:15 y 0:20 plantas por maceta con volumen de 8 dm3 de sorgo dulce (cultivares BRS 506, BRS 509 o BRS 511) contra B. pilosa. Cincuenta días después de la emergencia, se evaluaron el área foliar de la planta (LA), la masa seca de los brotes (MS), la fotosíntesis (A) y la transpiración (E). La capacidad competitiva se analizó utilizando el método de análisis gráfico, construyendo diagramas basados en la productividad total y relativa. También se determinaron la competitividad, el coeficiente de agrupamiento y la agresividad. Los cultivares de sorgo, en general, fueron menos competitivos en todas las proporciones de B. pilosa. Hubo pequeñas diferencias en la capacidad competitiva entre los cultivares de sorgo; BRS 509 demostró ser ligeramente más competitivo que BRS 506 y BRS 511 frente al B. pilosa a. Sin embargo, es poco probable que esto proporcione una ventaja competitiva para BRS 509 en los campos de producción, por lo que B. pilosa a debe controlarse de manera eficiente al principio del ciclo de cultivo para evitar pérdidas de productividad, independientemente del cultivar de sorgo.

ABSTRACT Among the weeds that interfere with the growth and development of sweet sorghum, beggar ticks stands out, because it has a high competitive capacity for the available resources. This study aims to compare the competitive ability of sweet sorghum (Sorghum bicolor (L.) Moench) against hairy beggarticks (Bidens pilosa L.), as a function of cultivar and plant proportion. Experiments were conducted in a greenhouse in a completely randomized design with four replications and six treatments. Treatments were arranged in replacement series in the proportions of 100:0, 75:25, 50:50, 25:75, and 0:100% (sorghum:weed) equivalent to 20:0, 15:5, 10:10, 5:15 and 0:20 plants per pot with 8 dm3 capacity of sweet sorghum (cultivars ‘BRS 506’, ‘BRS 509’ or ‘BRS 511’) against hairy beggarticks. Fifty days after emergence, plant leaf area (LA), aboveground dry mass (DM), photosynthesis (A), and transpiration rates (E) were measured. Competitive ability was analyzed by using the graphical analysis method and building diagrams based on total and relative productivity. Competitiveness, clustering coefficient, and aggressiveness were also determined. Sorghum cultivars, in general, showed losses independently of the proportion of hairy beggarticks. Statistical analysis showed small differences in competitive ability among sorghum cultivars; ‘BRS 509’ was also demonstrated to be slightly more competitive than ‘BRS 506’ and ‘BRS 511’ against hairy beggarticks. This, however, is unlikely to provide a competitive advantage for ‘BRS 509’ in production fields, and hairy beggarticks should be efficiently controlled early in the crop cycle to avoid productivity losses, independently of the sorghum cultivar.

Resumo - O objetivo deste trabalho foi avaliar aspectos ecofisiológicos da germinação de sementes em biótipos de sagitária (Sagittaria montevidensis) resistentes e suscetível a herbicidas. O delineamento experimental foi o inteiramente casualizado. Em campos de arroz, foram colhidas sementes de dois biótipos resistentes (SAGMO 10 e SAGMO 32) e de um suscetível (SAGMO 35) aos herbicidas inibidores da acetolactato sintase e do fotossistema II. A liberação da dormência foi realizada com 2,0% de nitrato de potássio, escarificação química (1,0% de H2SO4 por 30 s) e mecânica (lixa), 10 ppm de ácido giberélico, embebição em água por 24 horas, banho-maria a 60ºC e um controle. Avaliaram-se a germinação às temperaturas de 10 a 40°C e a emergência de plântulas aos 0,0, 0,5, 1,0, 2,0, 4,0 e 5,0 cm de profundidade de enterrio. Todos os biótipos apresentaram germinação superior a 70% após escarificação mecânica. A maior taxa de germinação ocorre a 25,9°C para SAGMO 35, o biótipo suscetível, e a 26,2 e 26,5°C, respectivamente, para SAGMO 10 e SAGMO 32, biótipos resistentes. Para todos os biótipos, a maior emergência de plântulas ocorre em sementes posicionadas a 0,5 e 1,0 cm de profundidade de enterrio.

Abstract - The objective of this work was to evaluate the ecophysiological aspects of seed germination in California arrowhead (Sagittaria montevidensis) biotypes resistant and susceptible to herbicides. The experimental design was completely randomized. In paddy rice fields, seeds were collected from two biotypes that are resistant (SAGMO 10 and SAGMO 32) and from one that is susceptible (SAGMO 35) to acetolactate synthase and photosystem II inhibiting herbicides. Seed dormancy release was performed with 2.0% potassium nitrate, chemical (1.0% H2SO4 for 30 s) and mechanical (sandpaper) scarification, 10 ppm gibberellic acid, water imbibition for 24 hours, water bath at 60°C, and a control. Germination was evaluated at temperatures from 10 to 40°C and seedling emergence at 0.0, 0.5, 1.0, 2.0, 4.0, and 5.0 cm burial depths. All biotypes showed a germination higher than 70% after mechanical scarification. The highest germination rate occurs at 25.9°C for SAGMO 35, the susceptible biotype, and at 26.2 and 26.5°C, respectively, for SAGMO 10 and SAGMO 32, the resistant biotypes. For all biotypes, the highest seedling emergence occurs in seeds positioned at the 0.5 and 1.0 cm burial depths.

Abstract: Background: Ryegrass is considered an important weed in crops in the state of Rio Grande do Sul, Brazil, for being resistant to the herbicide glyphosate. Objective: This study evaluates ryegrass control by applying different spray volumes and doses of clethodim alone or in combination with glyphosate and/or 2,4-D. Methods: Two field experiments were conducted in a 5 x 3 factorial design. In experiment I, factor A consisted of clethodim (96 g a.i. ha-1); clethodim (96 g a.i. ha-1) + glyphosate (1,080 g a.e. ha-1); clethodim (96 g a.i. ha-1) + 2,4-D (1,047 g a.e. ha-1); clethodim (96 g a.i. ha-1) + glyphosate (1,080 g a.e. ha-1) + 2,4-D (1,047 g a.e. ha-1); and control without treatment. Factor B consisted of three spray volumes (40, 80, and 120 L ha-1). In the second experiment, factor A consisted of the same herbicides and their associations aforementioned and factor B consisted of three increasing doses of the herbicide clethodim (96, 192 and 288 g a.i. ha-1). The herbicides were applied at the milky stage of ryegrass grains. Ryegrass control at 10, 20, and 30 days after application (DAA) of herbicides and dry matter were evaluated. Results: Spray volume reduction did not interfere with ryegrass control by clethodim and glyphosate or clethodim, glyphosate, and 2,4-D at 30 DAA, but it did interfere with the application of clethodim alone or associated only with 2,4-D. Doses above 192 g a.i. ha-1 of clethodim alone or in mixture were efficient for ryegrass control. Conclusions: Greater clethodim doses and spray volume increased control of ryegrass at the milky grain stage and decreased the antagonism in the associations with 2,4-D.

Abstract Background Weed competition is one of the main constraints to rice yield. Objective Determine the period prior to interference (PPI) of barnyardgrass ( Echinochloa spp.) on the irrigated rice crop as a function of the application of the herbicide cyhalofop-butyl alone and associated with penoxsulam. Methods A field experiment was carried out in a randomized block design, with four replications. The treatments were arranged in a 2×7 factorial scheme, with factor A consisting of the herbicides cyhalofop-butyl and the mixture penoxsulam + cyhalofop-butyl, while factor B consisted of seven coexistence periods: 0, 7, 14, 21, 28, 35, and 120 days after rice emergence (DAE). The herbicides were applied in each of these periods. The analyzed variables were crop height and shoot dry mass of the rice and barnyardgrass, number of grains per panicle, thousand-grain weight, and yield. Results The presence of barnyardgrass competing for environmental resources negatively affected the analyzed variables and rice yield for all periods with a coexistence longer than 28 DAE. Barnyardgrass competition during the entire rice cycle (120 DAE) reduced the shoot dry mass of the crop. Conclusions The PPI termination was determined at 14 DAE for the mixture cyhalofop-butyl + penoxsulam and 29 DAE for cyhalofop-butyl alone.

Abstract Background Weeds compete with crops, demanding efficient control to avoid yield losses. Highly competitive cultivars are a cultural method that can increase weed suppression and reduce the effects of crop-weed competition. Objective The present study aimed to assess the competitive abilities of barley cultivars (crop) against black oat (weed) and their interference in crop physiology. Methods A preliminary additive experiment was carried out with increasing densities of barley and black oat to determine the minimal density from where there was no drier mass increasing per area. In the second experiment, a replacement series experiment, five plant proportions (100:0; 75:25; 50:50; 25:75, and 0:100) of the crop were used and the competitor was installed. Fifty days after the emergence, morphophysiological and physiological variables, as well as their respective relative competitiveness indexes, relative clustering coefficient, and species aggressiveness, were all assessed. Results The variables associated with the photosynthesis were dependent on the cultivar. BRS Cauê was the cultivar that performed better against black oat, with an increase in the overall photosynthetic rate, due to a smaller leaf area loss, as the competition increased. BRS Brau reduced the photosynthesis into smaller proportions for the competitor. The water use was not impacted to the same extent as photosynthesis. Conclusions BRS Cauê was the most competitive cultivar, suffering the lowest impact of competition with black oat.

RESUMO A carência de herbicidas registrados para o controle de plantas daninhas, em sorgo sacarino, torna-se fator limitante à produção. Objetivou-se avaliar a seletividade de herbicidas em sorgo sacarino e a eficiência no controle de plantas daninhas. O delineamento experimental foi de blocos ao acaso, com quarto repetições. Os tratamentos incluíram cultivares de sorgo sacarino (BRS 506, BRS 509 e BRS 511) e herbicidas aplicados isoladamente em pré-emergência (atrazine - 1.500 g ha-1; atrazine + s-metolachlor - 1.665 g ha-1 + 1.035 g ha-1; flumioxazin - 50 g ha-1; s-metolachlor - 1.440 g ha-1) e pós-emergência (tembotrione - 100,8 g ha-1) e de forma sequencial em pré e pós-emergência (atrazine + s-metolachlor + tembotrione - 1.665 g ha-1 + 1.035 g ha-1 + 100,8 g ha-1; atrazine + tembotrione - 1.500 g ha-1 + 100,8 g ha-1; flumioxazin + tembotrione - 50 g ha-1 + 100,8 g ha-1), mais duas testemunhas, uma capinada e outra sem capina. A fitotoxicidade ao sorgo foi de 98,0 %, 98,0 % e 100 % de tembotrione; 100 %, 98,7 % e 100 % de flumioxazin + tembotrione; 100 %, 100 % e 100 % de atrazine + s-metolachlor + tembotrione; e 98,7 %, 98,7 % e 99,7 % de atrazine + tembotrione, respectivamente para as cultivares BRS 509, BRS 506 e BRS 511. Tembotrione, flumioxazin + tembotrione, atrazine + s-metolachlor + tembotrione e atrazine + tembotrione apresentaram bom controle de Ipomoea indivisa, Digitaria ciliaris e Urochloa plantaginea, porém, não demonstraram seletividade às cultivares de sorgo. O atrazine, de modo geral, apresentou maior seletividade aos componentes de rendimento das cultivares BRS 509 e BRS 506.

ABSTRACT The lack of registered herbicides for weed control in sweet sorghum has been a limiting production factor. This study aimed at evaluating the selectivity of herbicides in sweet sorghum and weed control efficiency. A randomized blocks design, with four replications, was used. Treatments consisted of sweet sorghum cultivars (BRS 506, BRS 509 and BRS 511) and herbicides applied alone at pre-emergence (atrazine - 1,500 g ha-1; atrazine + s-metolachlor - 1,665 g ha-1 + 1,035 g ha-1; flumioxazin - 50 g ha-1; s-metolachlor - 1,440 g ha-1) and post-emergence (tembotrione - 100.8 g ha-1) and sequentially at pre- and post-emergence (atrazine + s-metolachlor + tembotrione - 1,665 g ha-1 + 1,035 g ha-1 + 100.8 g ha-1; atrazine + tembotrione - 1,500 g ha-1 + 100.8 g ha-1; flumioxazin + tembotrione - 50 g ha-1 + 100.8 g ha-1), plus two controls, one weeded and one unweeded. The phytotoxicity rate to sorghum was 98.0 %, 98.0 % and 100 % for tembotrione; 100 %, 98.7% and 100 % for flumioxazin + tembotrione; 100 %, 100 % and 100 % for s-metolachlor + atrazine + tembotrione; and 98.7 %, 98.7 % and 99.7 % for atrazine + tembotrione, respectively to the BRS 509, BRS 506 and BRS 511 cultivars. Tembotrione, flumioxazin + tembotrione, atrazine + s-metolachlor + tembotrione and atrazine + tembotrione showed a good control rate of Ipomoea indivisa, Digitaria ciliaris and Urochloa plantaginea, but did not present selectivity to the sorghum cultivars. Atrazine, in general, showed higher selectivity to the yield components of the BRS 509 and BRS 506 cultivars.

O experimento foi conduzido com o objetivo de estimar a variação do banco de sementes viáveis de arroz vermelho (Oryza sativa L.), em três sistemas de semeadura de arroz (O. sativa L.) irrigado (semeadura convencional, direta e com sementes pré-germinadas), após três anos de cultivo na mesma área, em São Borja, RS, em solo classificado como Planossolo, com infestação média de 150 plantas de arroz vermelho por m² antes da instalação do experimento. A coleta do solo para estimativa do banco de sementes de arroz vermelho foi realizada com um trado cilíndrico de metal de 10cm de diâmetro. Foram realizadas amostragens de solo, com 12 amostras por parcela em duas profundidades (0-1cm e 1-10cm), para retirar os grãos de arroz vermelho, submetê-los ao teste de tetrazólio e determinar sua viabilidade. O experimento foi um bifatorial em blocos ao acaso, com três repetições, com os sistemas de semeadura de arroz como fator principal e as profundidades de coleta como fator secundário. Os dados demonstraram que o número de sementes viáveis de arroz vermelho no solo foi maior na área onde o arroz foi cultivado no sistema de semeadura convencional (1994 sementes/m²), com valores intermediários para o sistema de semeadura direta (597 sementes/m²) e menores valores para o sistema de semeadura com sementes pré-germinadas (93 sementes/m²). Assim, demonstra-se que a semeadura de arroz no sistema de sementes pré-germinadas favorece o controle do arroz vermelho, mantendo a quantidade de sementes em densidades menores do que nos sistemas de semeadura direta e convencional.

An experiment was conducted aiming to estimate the variability of viable seeds of red rice (Oryza sativa L.) in soil under three rice (O. sativa L.) seeding systems: conventional, no-tillage and water seeded. It was located in São Borja, Rio Grande do Sul state, Brazil, in an albaqualf soil with an average of 150 red rice plants per square meter before establishing the experiment. In order to estimate the seed bank, soil samples were colected using a cylinder with 10cm diameter. Twelve samples were obtained in each plot at two soil depths (0-1cm and 1-10cm) and the seeds were submited to the tetrazolium test to assess its viability. The experiment was a bifatorial in a randomized block design with three replications, in which seeding systems were the main effect and sampling depth the secondary factor. The results indicated a greater number of viable red rice seeds under conventional system (1,994 seeds m²), intermediate values for the no-tillage system (597 seeds m²), and lower numbers under the water-seeded system (93 seeds m²). Therefore, it was demonstrated that rice seeded in water-seeded system favors control of red rice, mantaining the quantity of red rice seeds in lower densities than under the conventinal or no-tillage systems.

O controle de plantas daninhas do tipo gramíneas constitui-se em grande problema nos sistemas de cultivo mínimo, requerendo aplicações eficientes de herbicidas. Nesse sentido, parâmetros de tecnologia de aplicação como volume de calda, tamanho de gota e concentração herbicida exercem grande influência sobre a atividade desses produtos. O objetivo desse trabalho foi investigar os efeitos das interações da dose herbicida, sua concentração na solução e o volume do veículo diluente, sobre a eficiência do herbicida sulfosate, usando-se arroz como espécie reagente. O experimento foi conduzido durante a safra agrícola de 1994/95 na Estação Experimental do Arroz do IRGA, em Cachoeirinha, RS. Foram testados 18 tratamentos, constituídos por cinco doses de sulfosate (1,7; 2,3; 3,0; 4,0 e 4,7 l/ha de produto formulado); cinco volumes de diluente (85; 115; 150; 200 e 235 l/ha) e cinco concentrações de produto na calda (1,2; 1,5; 2,0; 2,6 e 3,3% v/v). Em cada condição um desses parâmetros era fixado e os outros dois variavam. Ao se manter constante o volume de calda, não houve diferenças, na última avaliação, entre as doses 3,0; 4,0 e 4,7 l/ha de sulfosate, quando todas alcançaram nível ao redor de 90% de controle do arroz. Já quando se manteve constante a concentração herbicida, as respostas às doses foram não significativas. Apenas na última avaliação observou-se desempenho inferior da menor dose. Na terceira condição, quando se manteve constante a dose herbicida, observou-se que o sulfosate foi mais atuante quando aplicado nas maiores concentrações. Foram alcançados níveis de controle ao redor de 90% com doses de sulfosate de 3 l/ha ou superiores, ou com concentrações herbicidas de 2% ou maiores. Isso demonstra que parâmetros de tecnologia de aplicação de sulfosate podem ser alterados no sentido de se obter maior eficiência na sua ação.

Control of weed grass species constitutes a great problem in reduced tillage systems, requiring efficient herbicide application. In this sense, application parameters like spray volume, dropplet size, and herbicide concentration may exert great influence on activity of these products. The objective of this research was to investigate the interaction effects of herbicide rate,herbicide concentration, and diluent volume, on sulfosate efficiency, using rice as test plant. The experiment was conducted during the 1994/95 growing season at the IRGA Rice Experimental Station, in Cachoeirinha, RS, Brazil. Eighteen treatments were tested, performed by five sulfosate rates (1.7; 2.3; 3.0; 4.0; and 4.7 l/ha of formulated product), five diluent volumes (85; 115; 150; 200; and 235 l/ha), and five product concentrations in spray solution (1.2; 1.5; 2.0; 2.6; and 3.3 % v/v). In each condition, one of these parameters was fixed, whereas the other two varied. When maintained spray volume constant, there was no difference, at the last evaluation, among sulfosate rates of 3.0; 4.0; and 4.7 l/ha, when all these reached rice control around 90%. When herbicide concentration was maintained constant, the responses to herbicide rates were not significant.In the third condition, when herbicide rate was fixed, it was observed that sulfosate action increased at higher concentrations. Control levels around 90% were reached with herbicide concentration of 2% or higher. This demonstrates that application parameters of sulfosate may be modified in order to obtain greater efficiency in its action.

Em 1990, 91 e 92 foi conduzido ensaio na Faculdade de Agronomia da UFRS, em Porto Alegre, RS, cujo objetivo foi investigar os efeitos de herbicidas aplicados durante a fase reprodutiva de quinquilho (Datura stramonium). Foram testados dois compostos imidazolinonas (imazaquin e imazethapyr) e duas sulfoniluréias (chlorimuron e metsulfuron) sobre a produção de sementes e viabilidade e germinação das sementes formadas. Todas as aplicações berbicidas realizadas no florescimento, exceto metsulfuron na meia-dose, reduziram em mais de 75% a produção de sementes. As aplicações herbicidas efetuadas no florescimento de quinquilho reduziram em 76% o número de sementes por planta em comparação aos tratamentos aplicados no enchimento de grãos. Na avaliação da viabilidade das sementes não se constatou efeitos dos herbicidas testados. Herbicidas aplicados na fase reprodutiva de quinquilho permitiram reduzir a perpetuação da mesma por diminuir a produção de suas sementes.

A trial was conducted in 1990, 91 and 92 at Federal University of Rio Grande do Sul, in Porto Alegre, RS, Brazil, to investigate the effects of herbicides applied at the reproductive period of jimsonweed (Datura stramonium). Two imidazolinones (imazaquin and imazethapyr) and two sulfonylureas (chlorimuron and metsulfuron), which were tested for their effect on the number of seeds produced, seed viability and seed germination. All compounds applied at flowering stage, except half rate of metsulfuron, reduced by more than 75% the number of seeds produced. Herbicide applications at flowering stage reduced seed production by 76% in comparison with plants sprayed at grain filling stage. Jimsonweed seed viability was not affected by the treatments. Herbicides applied during jimsonweed reproductive stage reduce its survival by decreasing seed production.

Em 1990, 91 e 92 foi conduzido experimento na Faculdade de Agronomia da UFRS, em Porto Alegre, RS, com o objetivo de avaliar os efeitos de herbicidas aspergidos durante a fase reprodutiva em balãozinho (Cardiospermum halicacabum), corriola (Ipomoea grandifolia) e quinquilho (Datura stramonium). Foram testados dois compostos imidazolinonas (imazaquin e imazethapyr) e duas sulfoniluréias (chlorimuron e metsulfuron), e avaliadas as áreas foliar e cotiledonar, estatura e matéria seca das plântulas da geração seguinte. Em quinquilho, as áreas foliar e cotiledonar das plântulas aspergidas não diferiram da testemunha. Já as estaturas de balãozinho e quinquilho foram afetadas pelos herbicidas: em quinquilho, especialmente por clorimuron; em balãozinho, além de clorimuron, também por metsulfuron. Diversos tratamentos afetaram a matéria seca total ou de segmentos de plântulas de quinquilho. Em corriola não se constataram efeitos dos tratamentos herbicidas nas variáveis avaliadas. De modo geral, as características de plântulas da geração seguinte foram afetadas por alguns herbicidas aplicados na fase reprodutiva, como matéria seca em quinquilho e estatura em balãozinho, dependendo do produto, dose e época de aplicação.

A trial was conducted in 1990, 91 and 92 at Federal University of Rio Grande do Sul, in Porto Alegre, RS, Brazil, to investigate the effects of herbicides sprayed during the reproductive period of balloonvine (Cardiospermum halicacabum), morningglory (Ipomoea grandifolia), and jimsonweed (Datua stramonium). Two imidazolinones (imazaquin and imazethapyr) and two sulfonylureas (chlorimuron and metsulfuron) were tested and evaluated on foliar and cotyledonar areas, plant height, and dry matter of weed seedlings. ln jimsonweed, foliar and cotyledonar areas of seedlings did not differ from the control. However, the beights of ballonvine and jimsonweed seedlings were affected by the herbicides: in jimsonweed specially by chlorimuron, in baloonvine by chlorimuron, and metsulfuron. Multiple treatment influenced total plant dry matter and also dry matter of some components of jimsonweed plants. ln morningglory no effects of herbicide treatment on the traits evaluated were observed. ln general, characteristics of seedlings of the next generation were influenced by some herbicides applied during the reproductive period of the mother plants, for example dry matter in jimsonweed and height in baloonvine, depending on the compound and rate used and its time of application.